Variable resistance instrument



Dec. 18, 1956 E. c. ANTHONY ,77

VARIABLE RESISTANCE INSTRUMENT Filed April 19, 195 .4 2 SheetsSheet l I FIG. 5

FIG. 6

IN V EN TOR.

ELME/i C ANTHONY ATTORNEY Dec. 1956 E. c. ANTHONY VARIABLE RESISTANCE INS TRUMENT 2 Sheets-Sheet 2 Filed April 19, 1954 INVENTOR. ELMER C. ANTHONY BY United States Patent VARIABLE RESISTANCE INSTRUMENT Elmer C. Anthony, Rutherford, N. J., assignor to Benth'x Aviation Corporation, Teterboro, N. J., a corporation of Delaware Application April 19, 1954, Serial No. 423,909

16 Claims. (Cl. 201-56) This invention relates to variable electrical resistance instruments and especially to instruments of the potentiometer, rheostat or voltage divider type, in which a contact is moved along a resistance element.

An object of the invention is to provide a variable resistance instrument that can be effectively operated by automatic drive devices, such as synchros, that have very low power. Related objects are to provide a variable resistance instrument of this type that has very low operating friction, and one that is highly accurate and sensitive.

Another object is to provide a novel and efficient variable resistance device that is varied by rotary actuation through a plurality of turns, employing a helical resistance element.

A related object is to proved a more durable instrument of this type, and in particular one in which the resistance element may be of sufficient size to provide longer Wear. Features of the invention include improved constructions of the resistance unit, the sliding contact and the take-off connections. I

An additional purpose is to provide a variable resistance device that will retain its accuracy over a wide range of temperatures, both above and below ordinary room temperature.

Further objects are to provide a novel instrument of the type indicated that is advantageous for use as a potentiometer; one that constitutes an improved rheostat; and an instrument that functions as a sensitive and effective voltage divider.

Another object is to provide a variable resistance instrument having any or all of the indicated features, one that is readily manufactured, and is simple in construction and operation, compact and strong.

The foregoing and other objects and advantages of the invention will appear more fully from consideration of the detailed description which follows, in conjunction with the accompanying drawing, wherein one embodiment of the invention and a modification thereof are illustrated. It is to be expressely understood, however, that the drawing is for the purposes of illustration and description, and is not to be construed as defining the limits of the invention.

In the drawing:

Fig. 1 is a central longitudinal section through an embodiment of the invention, with parts shown in elevation; Fig. 2 is a transverse section on line 2--2 of Fig. 1; Fig. 3 is a transverse section on line 3-3 of Fig. 1;

Fig. 4 is an end view;

Fig. 5 is a side elevation partly in central longitudinal section of a modified form of resistance element; and

Patented Dec. 18, 1956 "ice rying a sliding contact that travels along said resistance unit. The resistance unit comprises a generally cylindrical spool or core 11 of suitable insulating material, having formed thereon a thread 12 with a flattened top provided with a longitudinal recess 13 arranged to fit an elongated resistance element 14 which projects above the surface of said recess. In the form illustrated in Figs.

1-3 the thread 12 has sloping side walls, and the resistance Fig. 6 is a similar view of another modified form of 7 for other purposes as desired. It comprises a central helical resistance unit surrounded by a rotary frame carelement 14 is a Wire.

Spool 11 is rigidly mounted on end plate 15, which as shown is formed of insulating material, and in the preferred embodiment is integral with spool 11. The ends of resistance element 14 are advantageously carried out through suitable bores extending lengthwise within spool 11 to the outer surface of end plate 15. As shown, the inner end portion 16 of resistance element 14 extends through longitudinal bore 17, while the outer end portion 18 of element 14 passes outwardly through bore 19.

Suitable tap connections to resistance element 14 may also be provided, two being shown in the illustrated arrangement. Inner tap lead 20 extends from the outer face of end plate 15 through bore 21, the inner end of which passes radially through a thread 12 into communication with an intermediate portion of resistance element 14, to which tap lead 20 is connected at 22. The outer tap lead 23 passes through a similar bore 24, whose end passes radially through a thread 12 into communication with another intermediate point 25 of resistance element 14, to which the end of outer tap lead 23 is connected. The ends 16 and 18 of resistance element 14, and the tap leads 20 and 23, are connected to lugs 26 mounted on plate 15, as shown in Fig. 4.

A contact sliding along resistance element 14 and totating on threads 12 is provided. In the form illustrated, a head plate 27 of insulating material has axially mounted therein a ball bearing 28 in which a drive frame 29 is rotatably mounted coaxial with spool 11. Frame 29, advantageously constructed of metal, includes a shaft 30 mounted in bearing 28 and connected to an integral drive plate 31 marginally carrying a drive ring 32. Metal cage rods 33 located on opposite sides of and parallel to spool 11 are mounted at one end in insulating bushings 31a in ring 32, and are fixed at the other end to annular metal take-off contact plate 34. Drive plate 31 and ring 32 also carry a ball bearing 35 in which a stub shaft 36 on the end of spool 11 is supported.

An arrangement for maintaining sliding contact with resistance element 14 is carried by a cylindrical follower block 37 (Figs. 1 and 2) of insulating material having longitudinal bores 38 at opposite sides slidably fitting rods 33. A contact strip 39 of spring metal has its opposite end portions located in transverse slots 40 in block 37, said end portions extending under and in spring contact with rods 33, and terminating in loops 41. The intermediate portion of contact strip 39 extends through a transverse bore 42 in block 37. Contact strip 39 is shaped so that it maintains the required frictional engagement with rods 33 without exerting excessive pressure. It is electrically connected by a slidable contact arrangement with resistance element 14, as by compres' sion coil spring 43 hearing against strip 39, slidably fitting a radial bore 44 in block 37 and bearing against a metal contact button 45 slidable in the passage and maintained by spring 43 in contact with resistance element 14. The central portion of block 37 is provided with drive threads 46 meshing with threads 12 of the spool 11. .Take-off contact springs 47 bearing yieldably. against contact plate 34 are mounted on the inner face of end plate 15, and are connected by lead 48 with lug 49 mounted on the outer face of plate 15.

A suitable housing and support is advantageously pro vided, being shown as a cylindrical metal housing 50 surrounding and spaced from the described mechanism and seated at its ends on plates and 27, being held in position thereon by screws 51.

in operation, rotation of shaft 34) will revolve drive frame 29, supported by ball bearing 23 for -iinimum friction, the adjacent end of spool 11 being supported and held in position by ball bearing 35. When shaft 39 is rotated, follower block 37 will travel alon spool 11, with contact button 45 sliding on resistance element 14. The point of contact will be maintained in electrical connection with lug if through button 45, springs 43 and 39, rods 35, contact plate and take-off springs 47. For use as a rheostat, connections may be made to lug 49 and the lug 26 connected to either the inner end 16 or the outer end 18 of resistance element 3.4. For use as a potentiometer, the potential source is connected across the lugs 26 connected to end portions 15 and 13 respectively, while the slider connection extends from lug 49. For use as a voltage divider, the intermediate connections are made to lugs 26 connected to tap leads and 23.

In the modified arrangement illustrated in Fig. 5 the thread 120 is rectangular in cross section, with a widened outer face having a recess 1311 that is rectangular in cross section and fits a resistance element 14:; in stri form, which projects to the necessary extent above thread 12a. The threads of follower block 37 are similarly contoured to conform to the threads 12a. This construction provides somewhat greater strength, good driving properties and substantially longer wear.

The modified form shown in Fig. 6 has the same advantages as that illustrated in Fig. 5, but illustrates the fact that the resistance element is not necessarily located at the thread apex. In this embodiment the rectangular resistance element 140 is located in a recess 13b in the space between turns of thread 12a.

The insulating material of which spool 11, plates 15 and 27 and follower block 37 are constructed may be any of the many well-known insulating materials, particularly the synthetic resins, having the required mechanical strength. It is also desirable, especially for instruments subjected to widely varying temperatures, to employ an insulating material of this type whose mechanical characteristics are not substantially affected by any temperatures within the range of use. In particular, the insulating material should be unaffected by the heat generated by passage of current through resistance element 14. Bushings 310 must possess the necessary strength to hold cage rods 33 in position, and advantageously are made of nylon.

Although but one embodiment of t e invention has been illustrated and described in detail, with two modifications thereof, it is to be expressly understood that the invention is not limited thereto. Various changes can be made in the design and arrangement of the parts without departing from the spirit and scope of the invention as the same will now be understood'by those skilled in the art.

I claim:

1. A variable electrical resistance instrument, comprising a support including a continuous screw thread, a resistance element extending along the apex of and insulated from the thread, a follower, including a screw thread meshing with the support thread and rotatable thereon, and a contact element mounted on the follower and slidably engaging the outer face of the resistance element.

2. A variable electrical resistance instrument, comprising a support of insulating material including a con tinuous screw thread, a resistance element extending along the apex of the thread, a follower, including a screw thread meshing with and rotatable relative to the support thread, and a contact element mounted on the screw thread, a resistance element extending along and insulated from the thread, a support unit mounting member engaging an end of the support unit, a follower including a screw thread meshing with and rotatable along the support unit thread, a contact element mounted on and insulated from the follower and slidably engaging the resistance element, a drive frame unit slidably engaging the follower and extending along the support, and a frame unit mounting member, one of said units being rotatable in its mounting member for relative rotation of the follower and support.

5. A variable electrical resistance instrument, comprising a cylindrical support including a continuous screw thread, a resistance element extending along and insulated from the thread, a support mounting member fixed to an end of the support, a follower including a screw thread meshing with and rotatable along the support thread, a contact element mounted on and insulated from the follower and slidably engaging the resistance element, a frame mounting member, and a drive frame slidably engaging the follower, extending along the support and rotatably mounted in the frame mounting member c'oaxially with said support.

6. A variable electrical resistance instrument, comprising a cylindrical support including a continuous screw thread, a resistance'elernent extending along and insulated from the thread, a support mounting member fixed to an end of the support, a follower including a screw thread meshing with and rotatable along the support thread, a contact element mounted on and insulated from the follower and slidably engaging the resistance element, a frame mounting member, a drive frame slidably engaging the follower, extending along the support and rotatably mounted in the frame mounting member coaxially with said support and a support mounting carried by the frame rotatably engaging the other end of the support.

7. A variable electrical resistance instrument, comprising a cylindrical support including a continuous screw thread, a resistance element extending along and insulated from the thread, a support mounting member engaging an end of the support, a follower including a screw thread meshing with and rotatable along the support thread, a contact element mounted on and insulated from the follower and slidably engaging the resistance element, a frame mounting, and a drive frame including a drive shaft extending through and rotatable in the frame mounting coaxially with the cylindrical support, and a drive member extending along the cylindrical support and slidably engaging the follower.

8. A variable electrical resistance instrument, comprising a cylindrical support including a continuous screw thread, a resistance element extending along and insulated from the thread, a follower including a screw thread meshing with and rotatable along the support thread, a rotatable drive frame including an electrically conducting drive member extending along the support and slidably engaging the follower, and a contact element mounted on the follower slidably engaging the resistance element and electrically connected to the drive member.

9. A variable electrical resistance instrument, com prising a cylindrical support including a continuous screw thread, a resistance element extending along and insulated from the thread, a follower including a screw thread meshing with and rotatable along the support thread, a rotatable drive frame including an electrically conducting drive member extending along the support and slidably engaging the follower, and a contact element mounted on the follower slidably engaging the resistance element electrically connected to the drive member, an annular conducting pick-off member connected to the drive element and coaxial with the support, and a take-off brush slidably engaging the pick-off member.

10. A variable electrical resistance instrument, comprising a cylindrical support of insulating material including a continuous screw thread, a resistance element extending along and insulated from the thread, a support mounting member engaging an end of the support, a follower of insulating material including a screw thread meshing with and rotatable along the support thread, a contact element carried by the follower and slidably engaging the resistance element, a contact element biasing spring on the follower, a mounting frame, a drive frame including a shaft rotatably mounted in and extending through the frame mounting coaxial with the support, a frame connected to the shaft including an electrically conducting drive member extending along the support, slidably engaging the follower and electrically connected to the contact element, an annular conducting take-off member carried by the drive member, and a take-off brush slidably engaging the take-off member.

11. A variable electrical resistance instrument, comprising a cylindrical support including a continuous screw thread, a resistance element extending along and insulated from the thread, and a follower including a screw thread meshing with and rotatable along the support thread, a contact element carried by the follower and slidably engaging the resitsance element, and a contact biasing spring carried by the follower.

12. A variable electrical resistance instrument, comprising a cylindrical support including a continuous screw thread, a resistance element extending along and insulated from the thread, and a follower of insulating material, including a screw thread meshing with and rotatable along the support thread, a contact element slidable in a radial bore in the follower and slidably engaging the resistance element, a compression coil spring in the bore bearing against the contact member, and a conducting member on the follower electrically connected to the spring.

13. A variable electrical resistance instrument, comprising a cylindrical support including a screw thread, a resistance element extending along and insulated from the thread, a follower including a screw thread meshing with and rotatable along the support thread, a contact member carried by the follower and slidably engaging the resistance element, and a conductive drive member slidably engaging the follower and electrically connected to the contact member.

14. A variable electrical resistance instrument, comprising a cylindrical support including a screw thread, a resistance element extending along and insulated from the thread, a follower of insulating material including a screw thread meshing with and rotatable along the support thread, a contact member carried by the follower and slidably engaging the resistance element, a conductive drive member slidably engaging the follower, and an electrical connection between the contact member and the drive member, including a spring carried by the follower and slidably bearing against the drive member.

15. A variable electrical resistance instrument, comprising a cylindrical support of insulating material including a screw thread having a longitudinal recess at its apex, a resistance element extending along and seated in the recess, a follower including a screw thread meshing with and rotatable along the support thread, and a contact member carried by the follower and slidably engaging the resistance element.

16, A variable electrical resistance instrument, comprising a cylindrical support of insulating material including a screw thread having a longitudinal recess extending along its apex, a resistance element extending along and seated in the recess, and a follower of insulating material, including a screw thread meshing with and rotatable along the support thread, and a contact member mounted in a radial bore in the follower and slidably engaging the resistance element.

References Cited in the file of this patent UNITED STATES PATENTS 2,150,502 Harrison et al Mar. 14, 1939 FOREIGN PATENTS 8,274 Great Britain Apr. 6, 1910 

